Linear generator with a swinging piston

ABSTRACT

An electromechanical energy converter for a gaseous or vaporous medium comprising a stator ( 1 ) with two pot-shaped stator members ( 1   a,    1   b ), each open at one end face and adjoining each other at these end faces, said stator members surrounding a working space ( 12 ) and forming a common magnetically permeated air gap ( 7 ) in which a coreless armature coil ( 25 ) is displaceably arranged. Arranged in the working space ( 12 ) is a freely oscillating piston ( 14 ) linked to the armature coil ( 25 ). Furthermore, at least one source ( 21   a,    21   b ) for the medium, two reaction chambers ( 66   a,    66   b ) each assigned to a head ( 15   a,    15   b ) of the piston ( 14 ) and control means ( 17   a,    19   a,    22   a,    23   a;    17   b,    19   b,    22   b,    23   b ) assigned to the reaction chambers ( 66   a,    66   b ) for self-control of the piston oscillations are provided, by means of which the reaction chambers ( 66   a,    66   b ) may be opened to the source ( 21   a,    21   b ) during the piston oscillations for accepting medium under pressure, and to the working chamber ( 12 ) for releasing expanded medium ( FIG. 11 ).

The invention concerns an electromechanical energy converter designed asa linear generator having a free piston.

In contrast to conventional electromechanical energy converters, lineargenerators with freely oscillating working pistons dispense with rotarymovements and the crank drives needed for these. The energy conversionis provided by the back and forth linear movement of a working piston,often known as a free piston. The conversion of the mechanical energyinto electrical energy takes place thereby that the working piston isprovided with a plurality of magnets of alternating polarity and isarranged in a coil surrounding it (DD 113 593, DE 43 15 046 A1, DE 19943 993 A1). A corresponding principle is applied to electromechanicalconverters that do not work as electrical generators, but as electricallinear motors (DE 41 07 530 A1) or that serve optionally for electricalor mechanical energy generation (EP 0 185 656 B1). Due to the pluralityof permanent magnets mounted on the working piston and the inertiacaused thereby, large accelerating and braking forces have to beapplied, which result in low working frequencies. Normally for theseso-called field displacers, magnet pairs arranged with mirror symmetryor rotational symmetry are used, in order, in the ideal case, to avoidlateral forces. Due to manufacturing tolerances, this is not fullyachievable, however and the bearings are increasingly loaded througheven the slightest wear. These loads then become exponentiated. Complexdesigns increase the proneness to faults, which militates againstmaintenance-free operation of the working piston over several years.

Energy converters of the aforementioned type have therefore become known(U.S. Pat. No. 4,532,431, WO 94/26019) whereby the working pistons arelinked solely by a coreless armature coil, displaceably mounted in theair gap between two pot-shaped stator members arranged mutually opposed.Although an arrangement of this type offers significant advantages withregard to the accelerating and braking forces to be applied, energyconverters of this type have previously not become established on themarket. A main reason for this may be seen in the fact that the pistonheads impinged upon by the gaseous or vaporous medium are displaceablymounted in chambers arranged outside the stator, whereby sealingproblems arise which militate against operation of the piston free fromfaults and servicing over several years. Furthermore, it is not possiblewith these energy converters without further difficulty to guide thegaseous or vaporous medium round a circuit, to realise a compact andspace-saving design, and to solve cooling problems arising duringoperation.

The technical problem to be solved by the present invention thereforeconsists in designing an electromagnetic energy converter of theaforementioned type such that, while avoiding the stated disadvantages,the occurrence of sealing problems are avoided and a simple space-savingdesign may be arrived at which enables very quiet operation over long,maintenance-free periods.

The fulfilment of this aim is given by the features of claim 1.

The invention brings with it the advantage that the gaseous or vaporousmedium is conducted, after its expansion, into the working spacesurrounded by the stator. This enables the creation of a compact, closedsystem with a common cooling space which may be used, on the one hand,for cooling the components of the electromechanical converter (fieldcoils, armature coil, etc.) and, on the other hand, for cooling andcondensation of the gaseous or vaporous medium. Further advantagesconsist therein that the piston may be designed short and withoutspecial bearings, which enables lasting, maintenance-free running of thepiston and no external chambers need to be provided, so that no sealingproblems can arise.

Further advantageous features of the invention are disclosed in thesubclaims.

The invention will now be described in greater detail using embodimentsillustrated in the drawings, in which:

FIG. 1 shows the basic structure of the stator of an electromagneticconverter according to the invention in a schematic longitudinalsection;

FIG. 2 shows a section along the line II-II in FIG. 1;

FIG. 3 shows, on a scale somewhat changed relative to FIG. 1, alongitudinal section through a working piston linked to an armature coilfor the converter according to the invention;

FIGS. 4 and 5 show schematic partial diagrams of two possibleembodiments of a device operated with the converter according to theinvention;

FIG. 6 shows a longitudinal section through an embodiment of a completeconverter;

FIGS. 7 and 8 show a schematic section through a valve of the converteraccording to FIG. 6 in a closed position and an open position;

FIGS. 9 and 10 show a partial view of the converter according to FIG. 6in two different operational positions of a working piston;

FIG. 11 shows a longitudinal section through a second embodiment of acomplete converter;

FIG. 12 shows an enlarged detail X of FIG. 6 with a supply line for acoolant and/or lubricant;

FIG. 13 shows a section along the line XIII-XIII in FIG. 9, and FIG. 14shows a section along the line XIV-XIV in FIG. 13.

According to FIGS. 1 and 2, an electromechanical energy converteraccording to the invention has a stator 1 with two pot-shaped statormembers 1 a and 1 b made of soft iron or similar. The stator member 1 acontains a central pole piece 3 coaxial with a longitudinal axis 2 ofthe converter and an outer pole piece 4 surrounding it coaxially inannular fashion. The central pole piece 3 is preferably formedsubstantially cylindrical. On the other hand, the outer pole piece 4 ispreferably designed as a hollow cylinder and closed by a base 5 at oneend. At the open side opposing the base 5 of the pot thus formed, thetwo pole pieces 3, 4 suitably border a planar end face. Between the polepieces 3, 4 is a peripheral annular gap. The stator member 1 b issuitably formed identical to the stator member 1 a and, like it, havingrotational symmetry about the longitudinal axis 2.

As FIGS. 1 and 2 also show, the two stator members 1 a, 1 b adjoin eachother with their end faces lying on the open sides along a plane ofsymmetry indicated by a line 6, so that on the one hand, they arearranged with mirror symmetry about the plane of symmetry 6 and, on theother hand, are arranged coaxial with the longitudinal axis 2. Theirgaps arranged between the pole pieces 3, 4 therefore continue to an airgap identified overall with the reference number 7.

In a region between the central pole piece 3 and the outer pole piece 4,the stator members 1 a, 1 b have recesses in which are arranged windings8 a, 8 b that are connected in a manner not shown in greater detail to adirect current source. The poling of the magnetic field generated by thewindings 8 a, 8 b is chosen such that, for instance, a north pole Nforms on the central pole piece 3 and on the outer pole piece 4, a southpole S forms (FIG. 1), although the polarity may also be reversed.Furthermore, it is clear that the stator 1 could also be excited bypermanent magnets, in which case the windings 8 a, 8 b would bedispensed with.

Finally, FIGS. 1 and 2 show that the central pole piece 3 of each statormember 1 a, 1 b is provided, on the one hand, with a central recess and,on the other hand, with slits 11 in a cruciform arrangement. Therecesses are arranged coaxial with the longitudinal axis 2, each closedat their outer end with one schematically indicated cover 10 a, 10 b andformed axially continuous, so that they form a passageway 9 runningbetween the covers 10 a, 10 b. The slits 11, however, run perpendicularto the plane of symmetry 6 and radially to the air gap 7 (FIG. 2), sothat they link it to the passageway 9. By this means, in the centralpole pieces 3, a coherent working space 12 comprising the passageway 9and the slits 11 and only indicated in FIG. 6 is formed.

A substantial advantage of the two similarly made mutually abuttingstator members 1 a, 1 b consists therein that outside the air gap 7, nostray fields arise. Rather, the field lines emanating from the twostator members 1 a, 1 b are squeezed back into the iron parts andtherefore made fully effective in the air gap 7, so that it is evenlymagnetically permeated over the entire length, leading to a high levelof efficiency.

FIG. 3 shows a freely oscillating piston 14 of the converter accordingto the invention to be arranged in the passageway 9. Like the passageway9, the piston 14 preferably has a circular cross-section and is formedin a central section as a tube 14 a. On its two ends, this tube 14 a isclosed by a piston head 15 a, 15 b and is mounted displaceable back andforth in two cylinder sections 16 a, 16 b, each with a sliding seating,whereby the cylinder sections 16 a, 16 b are sealed in the centralrecesses of the associated pole pieces 3 and fixed to them, forinstance, with screws. The cylinder sections 16 a, 16 b mayalternatively comprise a continuous cylinder, although for practicalreasons they are separated in order that each cylinder section 16 a, 16b may be individually removed axially for servicing and repair work andmay be installed.

In the example, the piston 14, usually designated as a free piston, hascoaxial guide shoulders standing outwards or sliders 17 a, 17 b ofreduced cross-section, which are mounted coaxially displaceable in guideopenings of end disks 19 a, 19 b arranged transversely in the cylindersections 16 a, 16 b. Furthermore, the piston 14 is sealed relative tothe cylinder sections 16 a, 16 b with the aid of circumferential seals20 a, 20 b standing out radially close to the piston heads 15 a, 15 bradially spaced from its periphery, so that between the piston heads 15a, 15 b and the associated covers 10 a, 10 b, compression chambers 21 a,21 b are produced. These serve to receive a gaseous or vaporous mediumin order to induce the piston 14 into a back and forth movement freelyoscillating in known manner or—if the piston is driven—periodically tocompress and expand the medium situated in the compression chambers 21a, 21 b in the manner of a compressor or similar. The control of themovement of the piston 14 may be carried out, as is explained in greaterdetail below based on FIG. 11, for instance, with the aid of controlslits 22 a, 22 b made in its outer jacket and arranged distributed roundits periphery, the end disks 19 a, 19 b and by outlet slits 23 a and 23b formed in the cylinder sections 16 a, 16 b, said outlets being formedon the ends of the cylinder sections 16 a, 16 b facing towards the planeof symmetry 6 and arranged distributed in the peripheral direction. Theparts 17 a, 17 b, 19 a, 22 a, 22 b, 23 a and 23 b represent the controlmeans of a slider valve control system, explained below. It is importantin this regard that the outlet slits 23 a, 23 b are open to the workingspace 12.

The piston 14 is provided in a central section with webs 24 projectingoutwards and arranged in cruciform manner, whose form and size is sodimensioned that they may be accommodated by an allocated guide slit 11and moved back and forth in it on moving the piston 14 back and forth.On their radially outer ends, the webs 24 are attached to the inside ofan armature coil 25 to be arranged coaxially in the air gap 7, the sizeand form of said armature coil being so dimensioned that it is able tojoin, in the manner of a plunger coil, in axial movements of the workingpiston 14 in the air gap 7.

The armature coil 25 is substantially coreless according to theinvention and is therefore of low weight, so that neither do largeacceleration forces have to be applied, nor do radial transverse forcesoccur on movement of the armature coil 25 in the air gap 7. Furthermore,the piston 14, the webs 24 and the armature coil 25 comprise a coherentunit which, due to the use of a coreless armature coil 25 may also bedesigned relatively light, particularly if the piston 14 and the webs 24are made, for instance, of aluminium, fibre composite material orsimilar. By this means, high working frequencies may be achieved in thepractical implementation.

As FIG. 4 shows schematically, the piston 14 is surrounded by twosprings 27 a, 27 b designed as helical springs, which are attached withtheir inner ends each to an allocated terminal of the armature coil 25,but which lead outwards with their outer ends out of the converter.Furthermore, the springs 27 a, 27 b are linked to the piston 14 audstationary parts in the working space 12, such that when the converteris not in operation, they define a central position of the piston 14 andthe armature coil 15, which is favourable for a starting or running-upphase of the converter. The springs 27 a, 27 b therefore serve both aselectrical connections for the armature coil 25, avoiding slidingcontacts or similar, and also for centring it.

In the example shown in FIG. 4, a converter 28 designed according to theinvention as shown in FIGS. 1 to 3 is illustrated as part of anelectrical generator or similar, which may be used for instance, in aone or two-family house for additional electrical generating. Inaddition, applications in isolated operation (in huts, yachts, mobilehomes or similar) or in countries without central electricity generationare also conceivable. In such cases, the converter 28 is operated withsteam generated, for instance, in a boiler 29 to the required pressureof, for instance, 30 bar to 50 bar and the required temperature ofbetween e.g. 200 C and 350 C. In this case, the boiler 29 is designed asan accessory component of a normal oil or gas burner 30 present anywayin heating systems for living accommodation, which may be used foroperating a normal oil or gas heating system and whose flame may also beused for generating steam.

The converter 28 is preferably provided with two circuits linked withinthe converter, which both conduct steam or water, A first circuit servesas the coolant and/or lubricant circuit. It contains a pump 31, whichdraws coolant and/or lubricant flowing through the working space 12 ofthe converter 28, in this case water, from a removal line 32 formed inthe stator 1 and feeds it to a heat exchanger 33 which, for instance,supports the heating of service water through a living accommodationheating system. The water cooled in the heat exchanger 33 is fed againto the converter 28 through a feed line 34 of the stator 1 as coolantand/or lubricant. The second circuit, on the other hand, contains a pump35, which also draws water out of the converter 28 through the removalopening 32, but feeds it directly to the vaporiser 29, where it isvaporised again and is fed to a connector 36 in the cover 10 a and/or 10b as a vaporous working medium. The steam serves to drive the piston 14,as explained below. Following the working operation, the steam condensesagain to water and is collected in the free space 12 (FIG. 1) like thewater used as coolant and/or lubricant and from there is fed again tothe removal line 32. Both circuits are therefore unified in a commonhousing formed by the stator members 1 a, 1 b and the covers 10 a, 10 band hermetically sealed against the outside.

The embodiment according to FIG. 5 differs from that according to FIG. 4only in that the pump 35, as described below, is replaced by at leastone piston pump installed in a bore in the central pole piece 3 andtherefore directly integrated into a converter 37. In the embodimentaccording to FIG. 5, in each of the two central pole pieces 3, a pistonpump 38 a, 38 b of this type is provided. In each case, one piston 39 a,39 b of the piston pump 38 a, 38 b is preferably attached to one of thewebs 24, whereby the pump stroke is synchronised with the stroke of thepiston 14. Otherwise, in FIG. 5 the same reference numbers are used asin FIG. 4.

FIGS. 6 to 10 show further details of the converter 28 shown onlyschematically in FIGS. 1 to 4, so that similar parts are identified withthe same numbers even where they show slight differences in comparisonwith FIGS. 1 to 4 and these differences are not of importance to theinvention.

As distinct from FIG. 3, the tube 14 a of the piston 14 is provided onthe axial ends with two piston heads 41 a, 41 b, each of which has atits outer ends a circumferential groove into which a sealing ring 42 anda piston ring 43 are inserted (FIG. 9). Both are held in the groove bydisks 44 lying against them from outside, whereby the two disks 44 aretensioned against the piston heads 41 a, 41 b by a rod 45 extendingthrough the piston heads 41 a, 41 b and nuts 46 screwed onto its endsand thereby attached to said piston heads. The sealing ring 42 may actas a sliding bearing and support the sealing effect of the piston ring43.

According to the embodiment illustrated in FIGS. 6 to 10, arranged ineach of the axially inner ends of the compression chambers 21 a, 21 bshown in FIG. 3 is a valve 47 a, 47 b, each of which lies with mirrorsymmetry to the plane of symmetry 6 and preferably designed identically,so that only the valve 47 b will be described in greater detail below.Both valves 47 a, 47 b serve the purpose of bringing about self-controlof the oscillations of the working piston 14.

As is shown in particular by FIGS. 7, 8 and 9, the valve 47 b contains asubstantially hollow cylindrical housing 48 which is set coaxially andin sealed manner into the axially outer end of the cylinder section 16 band ends at the cover 10 b. Situated coaxially in the housing 48 andfixed rigidly by means of a screw fixing 49 on the cover 10 b is asubstantially cylindrical guide body 50 on which is mounted a valve body51 designed as a hollow cylinder displaceable parallel to thelongitudinal axis 2. The valve body 51 contains a cylindrical jacket 52(FIGS. 7, 8), which gives way towards the piston head 41 b along aconical section 53 to a cylindrical end section 54 of reducedcross-section in which a plurality of openings 55 is formed. On its endremote from the end section 54, the valve body 51 is provided with ashoulder section 56 angled perpendicular to the longitudinal axis 2,which gives way to a guide section 57 arranged coaxially with thelongitudinal axis 2. This is displaceably mounted on the guide body 50by means of a sliding bearing 58, which also serves as a seal, fixed inthe peripheral surface of the guide body 50 and tensioned in thedirection of the associated piston head 41 b by means of at least onecompression spring 59 supported between the shoulder section 56 and thecover 10 b.

The housing 48 is provided on its end facing towards the piston head 41b with a peripheral valve seating 60, whereby the arrangement is suchthat in a closed position of the valve 47T (FIG. 7) the valve body 51 ispressed with its conical section 53 against the valve seating 60 and isheld in this closed position by the compression spring 59.

The connector 36 offset laterally from the longitudinal axis 2 in FIGS.7 to 9 serves to introduce the gaseous or vaporous medium coming, forinstance, from the vaporiser 29 (FIG. 4) into the compression chamber 21b surrounded by the housing 48. The chamber surrounds the guide body 50and the valve body 51 in annular fashion and extends axially as far asthe valve seating 60. If the valve 47 b is in the closed positionaccording to FIGS. 6, 7 and 9, the medium is unable to leave thecompression chamber 21 b, so that a reaction chamber or expansionchamber 61 b axially enclosed in front of the valve 47 b by the cylinder16 b remains substantially unpressurised. In this case, the openings 55are all on a site within the reaction chamber 61 b lying in the axialdirection to the left of the valve seating 60.

The valve body 51 may be pushed against the pressure of the compressionsprings 59 in FIG. 9 to the right into an open position apparent fromFIGS. 8 and 10, whereby its guide section 57 slides on the slidingbearing 58. In the open position, the conical section 53 is lifted offthe valve seating 60, whereby simultaneously the openings 55 come to lieat least partially on the right side of the valve seating 60 in FIG. 8,as is indicated in FIG. 8 for an opening 55 a. As a result, the gaseousor vaporous medium may now flow in the direction of the arrows drawn inFIG. 8 out of the compression chamber 21 b through the openings 55 andthe end section 54 into the adjoining reaction chamber 61 b.

The valve arrangement containing the valve 47 a, which is arranged onthe opposing side—the left in FIG. 6—of the piston 14, iscorrespondingly designed, though with mirror symmetry. Furthermore, theparts 23 a, 23 b, 47 a, 47 b represent the control means of a valvecontrol system, whereby the outlet slits 23 a, 23 b are again open tothe working space 12.

The mode of operation of the converter described on the basis of FIGS. 6to 10 is substantially as follows:

In the rest position, the piston 14 and the armature coil 25 are in acentral position created by the springs 27 a, 27 b (FIGS. 4, 5) in whichboth valves 47 a, 47 b are in the closed position. The converter isstarted in that a current is passed through the armature coil 25 fromoutside, which is dependent upon the load associated with the armaturecoil 25 and the power at which the current windings 8 a, 8 b areoperated. The armature load may be adapted in advance depending upon thepressure of the working medium prevailing in the compression chambers 21a, 21 b such that following the start-up process, optimum running of thepiston 14 is achieved. Usually, a single defined stroke induced by thismeans suffices to bring the converter into motion, whereupon the currentflow to the armature coil 25 is switched off. The required calculationsare preferably carried out in a special starting box to which, formonitoring purposes, the present stroke position may be passed, measuredfor instance, with two stroke sensors 62 (FIG. 5) assigned to the piston14 or the webs 24 or the armature coil 25.

It is assumed that the piston 14 moves to the right in FIGS. 6 to 10. Itthen reaches the end of its stroke close to the valve 47 b, whereby anyexpanded gas residues in the reaction chamber 61 b are compressed andejected through the still open outlet slit 23 b of the cylinder section16 b into the working space 12. Shortly thereafter, the outlet slit 23 bis closed by the piston head 41 b and the reaction chamber 61 b issealed by the piston ring 43.

As soon as the piston head 41 b, with the constant reduction of thereaction chamber 61 b, makes contact with the end section 54 of thevalve 47 b, the valve body 51 is moved to the right against the force ofthe springs 59 (FIG. 10). For this purpose, the piston head 41 b may beprovided with a contact plate 63 (FIGS. 9, 10) adapted to the form ofthe end section 54 of the valve body 51, said contact plate beingarranged between the disk 44 and the nut 46. The right dead-centre pointof the working piston 14 is reached (in FIG. 10), for instance, when thenut 46 makes contact with the bottom of a recess in the guide body 50.

As a result of the movement of the valve body 51 as described, the valve47 b is opened. The reaction chamber 61 b is now open to the compressionchamber 21 b, so that the medium present in the latter may pass throughthe at least partially freed openings 55 into the reaction chamber 61 band may perform work there in that it pushes the piston 14 in FIG. 10 tothe left and thereby enlarges the reaction chamber 61 b once again. Thiscontinues initially until the valve body 51 is returned by the springs59 into its closed position again.

On the left side of the converter in FIG. 6, corresponding processes aretaking place. Through movement of the piston 14 to the right, the valve47 a is brought into the closed position and the reaction chamber 61 aenlarged ever more until the piston head 41 a finally frees the outletslits 23 a in the cylinder section 16 a and the reaction chamber 61 a islinked to the working space 12, in order to allow the expanded medium toflow into the working space 12. If therefore the piston 14 moves left asdescribed, at the start of tis movement stroke, initially any residualgas left in the reaction chamber 61 a is released through the outletslits 23 a into the working space 12, whereupon the outlet slits 23 aare closed and the reaction chamber 61 a is sealed by the seal 42 andthe piston ring 43 of the piston head 41 a. The processes described thenrepeat, since the piston 14 now moves in the direction of the left-handdead-centre point, thereby opening the valve 47 a and is againaccelerated to the right by the steam arising in the left-handcompression chamber 21 b. The reaction chambers 61 a, 61 b each serve inthis process as a buffer or gas spring, since by correct dimensioningand arrangement of the outlet slits 23 a, 23 b, they ensure that thepiston 14 does not impact hard at its dead-centre points against theguide bodies 50 of the valves 47 a, 47 b or other stationary part of theconverter.

Since the armature coil 25 is firmly attached via the webs 24 to thepiston 14, it is moved back and forth within the stator 1 in the rhythmof the piston 14, whereby in known fashion an alternating electricalcurrent is generated, which may be tapped off by means of the springs 27a, 27 b.

The embodiment according to FIG. 11 shows details of the converter 37designed according to FIGS. 1 to 3 and FIG. 5, so that the samereference numbers are used for the same parts even if these parts showslight differences compared with FIGS. 1 to 3 and FIG. 5.

In similar manner to FIG. 3, the piston 14 is provided at each end witha piston head 15 a and 15 b having sliders 17 a, 17 b directed axiallyoutwards in whose peripheral surfaces the control slits 22 a, 22 b areformed. The control slits 22 a, 22 b take the place here of the valves47 a, 47 b of the embodiments according to FIGS. 6 to 10 and togetherwith the end disks 19 a, 19 b and the outlet slits 23 a, 23 b, comprisea slider valve control system for self-control of the pistonoscillation. Otherwise, the control slits 22 a, 22 b are arranged on thesliders 17 a, 17 b such that during the back and forth movement of thepiston 14, they interact with the sling rings 64 a, 64 b extendinginwards and mounted in the end disks 19 a, 19 b.

A further difference from the embodiment according to FIGS. 6 to 10consists therein that the two piston heads 15 a, 15 b and the adjoiningsliders 17 a, 17 b are passed through by a continuous coaxial tube 65,which links the two compression chambers 21 a, 21 b in every position ofthe piston 14 so as to allow through-flow. Therefore only one of the twoconnectors 36 in the covers 10 a and 10 b is provided for feeding in thegaseous or vaporous working medium, whilst the other connector 36 isclosed. Depending upon the spatial circumstances, one or other of theconnectors 36 may be selected for feeding in the working medium. In anyevent, the working medium enters into the relevant compression chamber21 b on one side and, on the other side, also through the tube 65 intothe other compression chamber 21 a or vice versa, so that substantiallythe same gas or steam pressure prevails in both.

The operational method of the embodiment according to FIG. 11 issubstantially as follows.

After the starting procedure which takes place similarly to FIGS. 6 to10, the piston 14 is situated, for instance, according to FIG. 1I in itsleft-hand dead-centre position. In this position, the control slits 22 aare arranged on either side of the sealing ring 64 a and therefore openpartially to the compression chamber 21 a and partially to the reactionchamber 66 a, which is situated between the end disk 19 a and theassociated piston head 15 a. The pressurised medium may therefore enterin the direction of the arrow into the reaction chamber 66 a, therebyact on the piston head 15 a and move the entire piston 14 in FIG. 11 tothe right. After a distance dependent upon the axial length of thecontrol slits 22 a, these are situated entirely on the right side (inFIG. 11) of the sealing ring 64 a or the end disk 19 a, so that now onlythe medium in the reaction chamber 66 a is able to act on the pistonhead 15 a.

Similarly to the above description of the first embodiment, in thisphase the outlet slits 23 b on the opposing side are still open, so thatin a reaction chamber 66 b situated there, any residual expanded gas isable to be ejected through the outlet slits 23 b into the working space12. However, after a certain movement of the piston 14 to the right, theoutlet slits 23 b are closed by the associated piston head 15 b,whereupon the piston rings 20 b lie against the cylinder section 16 b.At the same time, the sealing ring 64 b still lies against theassociated right-hand slider 17 b, so that the reaction chamber 66 b ishermetically sealed and the gaseous or vaporous medium cannot enter it.

On further movement of the working piston 14 to the right, the left-handreaction chamber 66 a is increasingly enlarged, whereas the right-handreaction chamber 65 b is increasingly diminished, forming a buffer,whereby a hard impact of the piston head 15 b against the end disk 19 bis avoided. Shortly before this impact, the control slits 22 b alsoreach the region of the sealing ring 64 b, until finally they make aflow connection between the compression chamber 21 b and the reactionchamber 66 b and the movement direction of the piston 14 is thereforegradually reversed. The same process steps are then repeated asdescribed above for the left side of the converter 37.

As FIG. 11 also shows, the coolant and/or lubricant, which is introducedaccording to FIGS. 4 and 5 via the feed line 34 into the stator 1,passes via a channel 67 formed in said stator into an annular chamber 68with a radial depth, shown enlarged in FIG. 12 and situated between thepole pieces 4 and the armature coil 25. The coolant and lubricant cantherefore flow round the armature coil 25 and the pole pieces 4 in theperipheral direction, and thus cool these and the windings 8 a, 8 buntil it passes over the axial ends of the armature coil 25 into theworking space 12 and is removed from it via the removal line 32.

FIG. 11 also shows that arranged close to each of the compressionchambers 21 a, 21 b and beneath them, is one of the piston pumps 38 a,38 b according to FIG. 5.

Each of these piston pumps 38 a, 38 b contains a cylinder 69 formed inthe central pole piece 3 and made from a bore, above which is acollecting duct 70 provided on the floor of the working space 12, saidcollecting duct being connected to the cylinder 69 via an opening 71. Inthe cylinder 69, a piston (not shown in greater detail) may also moveback and forth with the associated piston rod 39 a, 39 b.

Part of the water used as coolant and lubricant and the water thatarises in the working space 12 through condensation of the steamentering through the outlet slits 23 a, 23 b is able to pass in thisembodiment via the collecting ducts 70 and the opening 71 into thecylinder 69 and out of it through a removal line 72 according to FIGS. 5and 11 to the vaporiser 29. The vaporiser therefore always has enoughwater available (e.g. 0.3 to 0.5 l/min) for generating the steam neededin the converter 37 without an additional external feed water pump beingrequired. It should be understood that the piston pumps 38 a, 38 b arealso provided with all the necessary valves or similar required forcarrying out the pump strokes performed in the rhythm of the movement ofthe piston 14.

FIGS. 13 and 14 show a preferred embodiment of the piston ring 43illustrated in FIG. 9, arranged between the piston head 41 b and thecylinder 16 b. In the interests of the longest possible service life andof simple servicing as soon as the wear limit is reached, the pistonrings 43 are made up from a series of overlapping mutually displaceableelements. The wedge-shaped elements 74 may advantageously be made fromsofter material than the circular segment-shaped elements 73. By thismeans, a lasting seal against the cylinder wall 16 b is ensured. As FIG.13 shows, first circular segment-shaped elements 73 alternate in thecircumferential direction with second wedge-shaped elements 74. In theembodiment three elements 73 and three elements 74 lying between themare provided. The wedge-shaped elements 74 are substantiallytrapezium-shaped, whereby a shorter side serving as a sealing surface 75coming to lie against the inner lining of the surrounding cylinder 16 bis rounded according to the internal contour of the cylinder section 16b, whilst the longer side 76 lies opposed to the associated cylinderhead 41 b. Between the two is a roof-shaped spring 77 formed forinstance as a leaf spring, which presses the element radially outwardsand keeps it in contact with the cylinder section 16 b. The two limbs 78and 79 of the element 74 linking the sides 75, 76 are formedwedge-shaped and run towards each other from the inside to the outside.

The circular segment-shaped elements 73 are also formed as sealingsurfaces 80 on their side facing away from the piston head 41 b andadapted to the inner contour of the cylinder section 16 b. They alsohave driving surfaces 81, 82 facing towards the limbs 78, 79 and lyingagainst these. This brings the advantage that the elements 74 which arepretensioned radially outwards by the springs 77 also act with theirlimbs or wedge surfaces 78, 79 upon the driving surfaces 81, 82 of theadjacent elements 73 and therefore also press their sealing surfaces 80radially outwards against the inner wall of the cylinder section 16 b.The elements 73, 74 are thereby automatically radially adjusted in theevent of wear of the sealing surfaces 75, 80.

The elements 73, 74 are arranged such that no gap arises on the slidingsurfaces. In the region of the elements 73, 74, these sliding surfacesare arranged overlapping as is shown in particular in FIG. 14. Eachelement 73, 74 has, for instance, half the wall thickness in anoverlapping zone 83 formed thereby.

The roof-shaped springs 77 are preferably clipped into appropriaterecesses in the elements 74 with eyes 84 provided in the roof region andthereby releasably linked to it, whilst the support surfaces of theirlimbs suitably lie in grooves formed in the jacket of the piston head 41b. Otherwise it is clear that the piston head 41 a may be provided witha corresponding piston ring 43 and that the piston rings 64 a, 64 baccording to FIG. 1 may be designed substantially like the piston rings43.

The cylinder sections are preferably made from steel or artificialcarbon infiltrated with antimony, whilst the piston ring elements 73, 74are made, for instance, from softer material, which wears fasterrelative to the cylinder sections. This ensures that on servicing, onlythe rings that are more easily changed have to be replaced.

The invention is not restricted to the embodiments described, which maybe altered in many ways, although the design described brings with itthe advantage of an arrangement that is very simple to realise and smallin size. For instance, in place of the described valve and slidercontrol systems, other control systems may also be provided. Inparticular, the piston 14, in place of being operated with steam, mayalso be driven with combustion gases or common fuels, such as petrol orsimilar, in which case, the gases introduced into the compressionchambers have to be ignited or exploded at the desired rate. It wouldalso be possible to design the sealing rings (e.g. 64 a, 64 b) providedin the cylinder sections 16 a, 16 b similarly to the piston ringsaccording to FIGS. 13 and 14 in order that they function like these andadjust themselves in the event of wear. However, in this case springs,for instance annular springs must be provided, acting radially inwardsinstead of radially outwards. It is also possible to leave out thespaces identified as compression chambers 21 a, 21 b all together andonly regard the connection ports 36 and/or hoses linked to these ascompression chambers. It is important for the function described onlythat the compression chambers 21 a, 21 b each represent sources orsupply devices for the medium under pressure and are opened to thereaction chambers at the right time points. The sources may thereforealso be realised with devices which directly generate the medium underpressure. Further, FIGS. 6 and 11, particularly show that the covers 10a, 10 b may also be arranged with axial separations from the bases 5 ofthe pole piece 4 and the cylinders 16 a, 16 b may be axially displacedfurther outwards. In this connection it is important only that theoutlet slits 23 a, 23 b open in some manner into the working space 12 inorder always to guide the expanded medium into it (see also FIGS. 4 and5), and that the covers 10 a, 10 b or the bases 5 are not perforated bymoving parts such as, for instance, the piston 14, which would lead tosealing problems. Finally, it is evident that the various features mayalso be used in other combinations than those shown and described.

1. Electromechanical energy converter for a gaseous or vaporous mediumcomprising a stator (1) with two pot-shaped stator members (1 a, 1 b),each open at one end face and adjoining each other at these end faceswith mirror symmetry along a plane of symmetry (6), said stator memberssurrounding a working space (12) and forming a common magneticallypermeated air gap (7), a coreless armature coil (25) displaceablyarranged in the air gap (7), a freely oscillating piston (14) arrangedin the working space (12) linked to the armature coil (25), at least onesource (21 a, 21 b) for the medium, two reaction chambers (61 a, 66 a;61 b, 66 b) each assigned to a head (15 a, 15 b; 41 a, 41 b) of thepiston (14) and control means (17 a, 19 a, 22 a, 23 a, 47 a; 17 b, 19 b,22 b, 23 b, 47 b) assigned to the reaction chambers (61 a, 66 a; 61 b,66 b) for self-control of the piston oscillations, and by means of whichthe reaction chambers (61 a, 66 a; 61 b, 66 b) may be opened to thesource (21 a, 21 b) during the piston oscillations for accepting mediumunder pressure, to the working chamber (12) for releasing expandedmedium.
 2. Energy converter according to claim 1, characterised in thatthe stator elements (1 a, 1 b) each have a central pole piece (3) and anouter pole piece (4) surrounding it.
 3. Energy converter according toclaim 1 or 2, characterised in that the stator members (1 a, 1 b) areformed with rotational symmetry about a longitudinal axis (2) of thepiston (14).
 4. Energy converter according to claim 3, characterised inthat the central pole pieces (3) are each provided with a passageway (9)coaxial with the longitudinal axis (2), surrounding the working spaceand accommodating the piston (14) and the armature coil (25) is linkedto the piston (14) via radial, inwardly projecting webs (24).
 5. Energyconverter according to claim 4, characterised in that inserted in sealedmanner in every passageway (9) is a closed cylinder section (16 a, 16 b)coaxial with the longitudinal axis (2) and closed to the outside with acover (10 a, 10 b) and the piston (14) is provided on each of its endswith a piston head (15 a, 15 b; 41 a, 41 b) in an assigned cylindersection (16 a, 16 b) sealed and displaceably mounted, such that betweeneach of the covers (10 a, 10 b) and the associated piston head (15 a, 15b; 41 a, 41 b), a compression chamber comprising the source (21 a, 21 b)of the gaseous or vaporous medium comes into existence.
 6. Energyconverter according to claim 5, characterised in that at least one ofthe covers (10 a, 10 b) is provided with a connector (36) for supplyand/or removal of the medium.
 7. Energy converter according to claim 5or 6, characterised in that the two compression chambers (21 a, 21 b)are linked together so as to permit flow, via a hollow space (45)passing through the working piston (14).
 8. Energy converter accordingto one of the claims 1 to 7, characterized in that the control means (17a, 19 a, 22 a, 23 a, 47 a; 17 b, 19 b, 22 b, 23 b, 47 b) are designed inthe manner of a valve and/or slider valve control system.
 9. Energyconverter according to claim 8, characterised in that the control means(17 a, 19 a, 22 a, 23 a, 47 a; 17 b, 19 b, 22 b, 23 b, 47 b) have outletslits (23 a, 23 b) arranged on the axially inner ends of the twocylinder sections (16 a, 16 b) for the medium and the piston heads (15a, 15 b; 41 a, 41 b) have sealing means (20 a, 20 b; 43) assigned tothem.
 10. Energy converter according to claim 8 or 9, characterised inthat the valve control system contains a valve (47 a, 47 b) arranged ineach of the cylinder sections (16 a, 16 b) and actuatable by theassociated piston head (41 a, 41 b).
 11. Energy converter according toclaim 8 or 9, characterised in that the slide valve control system hascontrol slits (22 a, 22 b) formed in the periphery of the piston heads(15 a, 15 b) and the cylinder sections (16 a, 16 b) are provided withsealing means (64 a, 64 b) assigned to said cylinder sections. 12.Energy converter according to one of the claims 1 to 11, characterisedin that the armature coil (25) is linked to at least one spring (27 a,27 b) serving both for current supply and removal and for centring. 13.Energy converter according to one of the claims 1 to 12, characterisedin that the stator (1) has at least one feed line or removal line (34,32) opening into the working space (12) for feeding or removal of acoolant and/or lubricant.
 14. Energy converter according to claim 13,characterised in that the removal line (32) is provided with at leasttwo outlets and the working space (12) is connected via a collectingduct (70) and a pump (38 a, 38 b) to at least one of the outlets. 15.Energy converter according to claim 14, characterised in that the pump(38 a, 38 b) is a piston pump having a pump piston (39 a, 39 b)integrated into the stator (1) and the pump piston (39 a, 39 b) islinked in driving manner to the working piston (14).
 16. Energyconverter according to claim 14 or 15, characterised in that it containsa vaporiser (29) having an outlet linked to the connector (36) of thecover (10 a, 10 b), that the medium is water vapour and that the firstoutlet linked to the pump (38 a, 38 b) is linked to an inlet of thevaporiser (29).
 17. Energy converter according to one of the claims 14to 16, characterised in that the coolant and/or lubricant is water andat least one second outlet is linked via a further pump (31) to a heatexchanger (33) connected to the feed line (34).
 18. Energy converteraccording to one of the claims 9 to 17; characterised in that at leastthe sealing means (20 a, 20 b; 43) allocated to the piston heads (15 a,15 b; 41 a, 41 b) comprise piston rings projecting radially from thepiston heads (15 a, 15 b; 41 a, 41 b) and assembled from mutuallydisplaceable elements (73, 74) arranged overlapping.
 19. Energyconverter according to claim 18, characterised in that the elements (73,74) comprise, in the peripheral direction of the piston rings (20 a, 20b; 43), alternating circular segment-shaped first elements (73) andsecond elements (74) radially pretensioned by springs (77), said secondelements having wedge surfaces (78, 79) acting on the first elements(73).
 20. Energy converter according one of the claims 1 to 19,characterised in that the armature coil (25) is linked to the piston(14) through slits (11) in the stator.